Autoimmune diseases manifest themselves in various forms, many of which are devastating and life-limiting. Among the different kinds of autoreactivity are those in which antibodies play a dominant role, reflecting aberrant autoantigen-specific B cell activation. The long term objective of this proposal is to understand how serological autoantibodies arise. To achieve this goal, striking new findings from this laboratory concerning B cell production of osteopontin (Opn, SPP1, Eta-1) will be pursued. Osteopontin is a secreted cytokine (Secreted PhosphoProtein1, SPP1) produced by T cells (Early T cell Activation-1, Eta-1) that is strongly associated with autoimmunity in both human diseases and murine models. This laboratory has now shown that Opn is produced by B cells through the IL-4-induced alternate pathway for BCR signaling, which is Lyn- dependent, in conjunction with signaling via the classical pathway, which is Lyn-independent. The goals of this project are to understand how the alternate pathway operates, how the alternate pathway and the classical together produce Opn expression, and how B cell Opn relates to autoimmunity. The specific aims are to: 1) Identify Lyn sites that are specifically phosphorylated as a result of IL-4 treatment through mass spectrometry;2) Evaluate the structural features of Lyn that are required for the alternate pathway through mutational analysis;3) Determine the regulatory elements through which the alternate and classical pathways induce Opn expression by analyzing promoter sites and transcription factors with EMSA and ChIP assays;4) Elucidate the role of B cell-specific Opn in promoting serological autoimmunity through adoptive transfer experiments with trangenic and knock-out animals, combined with immunization to elicit anti-dsDNA antibody. This laboratory proposes that IL-4 produced during certain situations of immune stress, such as septic infection, allergic reaction, and worm infestation, induces the alternate pathway for BCR signaling, which in turn activates Opn expression, which in turn stimulates polyclonal B cell activation, which in turn triggers the production of anti-DNA antibodies and serological autoreactivity. The results of this work are expected to have great relevance to public health in two ways: a) Interference with elements of the alternate pathway, such as Lyn, should terminate Opn expression and thus diminish production of the cytokine driving autoimmunity;and, b) enhancement of the alternate pathway and Opn expression should facilitate polyclonal B cell activation and thereby ameliorate immune deficiency states.Project Narrative The work described in this proposal is designed to further the general and explicit understanding of the means by which the immune system becomes abnormally activated and produces antibodies that react with, and damage, a person's own tissues. A specific hypothesis regarding the production and role of a hormone-like substance thought to be involved in this process will be tested. Ideally, this research will result in identification of specific molecules whose inhibition would diminish the production of autoantibodies and hence improve the condition of patients afflicted with autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosis;conversely, enhancement of such molecules would be expected to stimulate key elements of the immune system and thereby improve the condition of patients afflicted with immune deficiency states.